Imports of server_standalone command

PathSynopsis
flagPackage flag implements command-line flag parsing.
fmtPackage fmt implements formatted I/O with functions analogous to C's printf and scanf.
github.com/pkg/sftpPackage sftp implements the SSH File Transfer Protocol as described in https://filezilla-project.org/specs/draft-ietf-secsh-filexfer-02.txt
ioPackage io provides basic interfaces to I/O primitives.
io/ioutilPackage ioutil implements some I/O utility functions.
osPackage os provides a platform-independent interface to operating system functionality.